Fault tolerant turbo-generator system

ABSTRACT

A turbo-generator system for generating propulsive electrical power for an aircraft includes an electric machine comprising: a rotor configured to be rotated by a gas-turbine of the turbo-generator system; a stator comprising: a first active section comprising first windings surrounding a first portion of the rotor; and a second active section comprising second windings surrounding a second portion of the rotor.

TECHNICAL FIELD

This disclosure relates to electric machines in hybrid electricaircraft.

BACKGROUND

A hybrid aircraft may include a combustion motor that generatesrotational mechanical energy, a generator that converts the rotationalmechanical energy into electrical energy, and electrical motors thatconvert the electrical energy into rotational mechanical energy to drivea propulsor (e.g., fan, propeller, etc.) of the aircraft.

SUMMARY

In one example, a turbo-generator system for generating propulsiveelectrical power for an aircraft includes an electric machinecomprising: a rotor configured to be rotated by a gas-turbine of theturbo-generator system; a stator comprising: a first active sectioncomprising first windings surrounding a first portion of the rotor; anda second active section comprising second windings surrounding a secondportion of the rotor.

In another example, a system for providing propulsive electrical powerfor an aircraft includes a first generator configured to output a firstplurality of alternating current (AC) electrical signals; a secondgenerator configured to output a second plurality of AC electricalsignals; a first set of rectifiers of a plurality of rectifiers, whereinthe first set of rectifiers are configured to convert the firstplurality of AC electrical signals into a first plurality of directcurrent (DC) electrical signals for output onto a first DC electricalbus of a plurality of DC electrical busses, wherein electrical currentof the first plurality of DC electrical signals is divided amongst thefirst set of rectifiers, and wherein each respective rectifier of thefirst set of rectifiers includes a respective contactor configured tode-couple a DC output of the respective rectifier from the first DCelectrical bus; and a second set of rectifiers of the plurality ofrectifiers, wherein the second set of rectifiers are configured toconvert the second plurality of AC electrical signals into a secondplurality of DC electrical signals for output onto a second DCelectrical bus of the plurality of DC electrical busses, whereinelectrical current of the second plurality of DC electrical signals isdivided amongst the second set of rectifiers, and wherein eachrespective rectifier of the second set of rectifiers includes arespective contactor configured to de-couple a DC output of therespective rectifier from the second DC electrical bus.

In another example, a system for providing propulsive electrical powerfor an aircraft includes a first generator configured to output a firstplurality of AC electrical signals; a second generator configured tooutput a second plurality of AC electrical signals; a first set ofrectifiers of a plurality of rectifiers, wherein the first set ofrectifiers are configured to convert the first plurality of ACelectrical signals into a first plurality of DC electrical signals foroutput onto a first DC electrical bus of a plurality of DC electricalbusses; and a second set of rectifiers of the plurality of rectifiers,wherein the second set of rectifiers are configured to convert thesecond plurality of AC electrical signals into a second plurality of DCelectrical signals for output onto a second DC electrical bus of theplurality of DC electrical busses, wherein each rectifier of theplurality of rectifiers includes a respective controller of a pluralityof controllers, and wherein the plurality of controllers are configuredto coordinate response to detected faults.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a system that includes fault tolerantelectrical generation, in accordance with one or more aspects of thisdisclosure.

FIG. 2 is a schematic diagram illustrating a cross-section of agenerator, in accordance with one or more aspects of this disclosure.

FIG. 3 is a chart illustrating an example arrangement of windings inslots of an active section of a generator, in accordance with one ormore aspects of this disclosure.

FIG. 4 is a block diagram illustrating a rectifier of a fault tolerantgeneration system, in accordance with one or more aspects of thisdisclosure.

FIG. 5 is a chart illustrating example responses to rectifier faults, inaccordance with one or more aspects of this disclosure.

FIG. 6 is a flowchart illustrating an example technique for faulthandling in a fault tolerant generation system, in accordance with oneor more aspects of this disclosure.

DETAILED DESCRIPTION

In general, this disclosure is directed to fault tolerant generation ofelectrical energy. In some scenarios, generation of electrical energymay be a safety critical function. For instance, in the context ofhybrid aircraft where electrical energy is used for aircraft propulsion,the generation of electrical energy may fulfill a safety criticalfunction, the failure of which may be classified with major severity insome aircraft (e.g., small fixed wing), and perhaps hazardous or evencatastrophic in others (e.g., eVTOL or urban air mobility). Redundantelectrical generation sources may be used for safety critical powerbuses in aircraft. However, full redundancy for propulsive power may notbe practical from a weight perspective due to the amount of powerrequired. To reduce weight at the component level and power systemlevel, it may be desirable for the generation system to be highfrequency (i.e., high speed) and high voltage, of which there are few tono examples in airborne applications (e.g., that have been certified byregulatory authorities). Power density requirements may necessitate afine balance between reducing margin in the equipment (e.g., windingtemperature vs. insulation limitations) while still maintaining adequatelife and reliability. The unique scenario of aircraft operation mayresult in high operational altitudes. However, operation at highaltitudes may place further burden on the insulation system as thebreakdown strength of air is reduced at such altitudes, increasingconcern for partial discharge or corona. The safety and reliability ofnewly fielded generation equipment becomes challenging due to the lackof pedigree in the design approaches listed above.

In accordance with one or more aspects of this disclosure, a system thatgenerates electrical energy that is used for propulsion may be madefault tolerant. For instance, the system may be made such that faultsmay occur without reducing the power output to zero. In this way, thesystem may tolerate faults while still generating electrical energy,enabling continued propulsion. As such, aspects of this disclosure mayimprove reliability of an electrical energy generation system withoutrequiring full redundancy (e.g., without requiring a full doubling ofcomponents such as a combustion motor).

As one example of how a system may be made fault tolerant, a stator mayinclude multiple active sections surrounding a common rotor. Forinstance, as opposed to only including a single active section thatgenerates an alternating current (AC) power signal, the stator mayinclude a first active section that generates a first AC power signaland a second active section that generates a second AC power signal.Each of the active sections may include multiple (e.g., two)electrically isolated three-phase winding sets. The system may includemultiple rectifiers, with two or more rectifiers for each activesection. The rectifiers for a particular active section may covert ACpower signals generated by the particular active section into one ormore direct current (DC) power signals that are output onto a particularDC electrical bus. As such, the system may include two DC electricalbusses that are each independently driven by an active section of arotor and multiple rectifiers. In this way, the system may tolerate afault in any one of the active sections or rectifiers and still outputelectrical energy.

As another example of how a system may be made fault tolerant,rectifiers may include integrated DC fault isolation components. Forinstance, where a system includes a plurality of rectifiers, each of theplurality of rectifiers may include contactors between an output of apower stage (e.g., an AC/DC converter) of the rectifier and a DC outputof the rectifier. A controller of a rectifier may open a contactor ofthe rectifier in the event of a fault in the rectifier. As the systemincludes multiple rectifiers, a current load may be distributed amongstthe multiple rectifiers. This may reduce the current load flowingthrough each rectifier, thereby reducing current requirement for thecontactors. In this way, this disclosure enables the use of lighterweight and/or more compact contactors. Furthermore, in some examples, acontroller of a power stage of a rectifier may be further tasked withcontrol of a contactor of the rectifier, thereby eliminating the need toinclude an additional contactor controller.

As yet another example of how a system may be made fault tolerant,various rectifiers of a system may perform a coordinated fault response.For instance, where a first rectifier and a second rectifier receive ACoutputs from a single generator, the first rectifier and the secondrectifier may perform a coordinated response to a fault detected ineither of the first rectifier or the second rectifier. As one example,responsive to detecting a fault in the first rectifier, a controller ofthe first rectifier may apply a three-phase short at the first rectifier(e.g., apply crowbar using switches of the first rectifier) and mayfurther cause a controller of the second rectifier to apply athree-phase short at the second rectifier (e.g., apply crowbar usingswitches of the second rectifier). By performing such a coordinatedresponse, the rectifiers may mitigate and/or prevent damage to thesingle generator (e.g., due to heating).

FIG. 1 is a schematic diagram of a system that includes fault tolerantelectrical generation, in accordance with one or more aspects of thisdisclosure. As shown in FIG. 1 , system 100 includes combustion motor102, generator 104, rectifiers 106A-106D (collectively, “rectifiers106”), control busses 110A and 110B (collectively, “control busses110”), low-voltage direct current (DC) busses 112A and 112B(collectively, “LVDC busses 112”), high-voltage DC busses 114A and 114B(collectively, “HVDC busses 114”), propulsion units 118A and 118B(collectively, “propulsion units 118”). System 100 may be included in,and provide propulsion to, any vehicle, such as an aircraft (e.g., fixedwing, tilt rotor, rotorcraft, etc.), a locomotive, or a watercraft.System 100 may include additional components not shown in FIG. 1 or maynot include some components shown in FIG. 1 . For instance, system 100may include an electrical energy storage system (ESS) configured toprovide electrical energy to various components of system 100.

Combustion motor 102 may consume fuel to produce rotational mechanicalenergy, which may be provided to generator 104 via drive shaft 103.Combustion motor 102 may be any type of combustion motor. Examples ofcombustion motor 102 include, but are not limited to, reciprocating,rotary, and gas-turbines.

Generator 104 may convert rotational mechanical energy into electricalenergy. For instance, generator 104 may convert rotational mechanicalenergy derived from combustion motor 102 (e.g., via drive shaft 103)into alternating current (AC) electrical energy. In some examples,generator 104 may include a single active section. For instance,generator 104 may include a single active section with a set of windingssurrounding a single rotor, the set of windings outputting AC electricalenergy (e.g., three-phase electrical energy). However, in such anarrangement, certain faults may result in a complete loss of electricalpower, which may not be desirable.

In accordance with one or more aspects of this disclosure, generator 104may divided into multiple active sections (e.g., sections that containelectromagnetic elements to produce power), such as active sections 105Aand 105B (collectively, “active sections 105”), on a single rotor/shaft.Each of active sections 105 may include a set of windings (e.g., awinding set) that surround the single rotor. For instance, activesection 105 may include first windings that surround a first portion ofa rotor connected to drive shaft 103 and second windings that surround asecond portion of the rotor connected to drive shaft 103 (e.g.,displaced along a longitudinal axis of the rotor). Each of activesections 105 may output separate AC power signals of AC power signals108A-108D (collectively, “AC power signals 108”). Further details of onexample of generator 104 are discussed below with reference to FIG. 2 .

In some examples, generator 104 may be a permanent magnet (PM)generator. For instance, first active section 105A and second activesection 105 may operate as PM generators. In some examples, system 100may not include a clutch configured to rotationally decouple the rotorof generator 104 from combustion motor 102 (e.g., a gas-turbine). Assuch, drive shaft 103 may be rotationally locked to the rotor ofgenerator 104.

The first windings and the second windings may each comprise arespective plurality of phase set windings that outputs a respective ACpower signal of AC power signals 108. For instance, the first set ofwindings of active section 105A may include a first plurality of phaseset windings including first phase set windings that output AC powersignal 108A and second phase set windings that output AC power signal108B. Similarly, the second set of windings of active section 105B mayinclude a second plurality of phase set windings including third phaseset windings that output AC power signal 108C and fourth phase setwindings that output AC power signal 108D.

The windings in an active section of active sections 105 may beoverlapping, but electrically isolated. For instance, first and secondphase set windings may be overlapping and electrically isolated.Similarly, third and fourth phase set windings may be overlapping andelectrically isolated. The phase set windings may be made in a mannersuch that the magnetic coupling between overlapping phase sets isminimized, which may allow rectifiers 106 to each operate independentlyas discussed below. Further details of one example of how the windingsmay be arranged are discussed below with reference to FIG. 3 .

Rectifiers 106 may be configured to convert AC electrical energy into DCelectrical energy. For instance, each of rectifiers 106 may convert arespective input AC power signal of AC power signals 108 into arespective output DC power signal of DC power signals 107A-107D(collectively, “DC power signals 107). As shown in FIG. 1 , rectifiers106 may include multiple rectifiers for each active section of activesections 105, such as a separate rectifier for each phase set ofwindings. As such, electrical current of an active section may bedivided amongst the first set of rectifiers. For instance, rectifiers106A and 106B may convert AC electrical energy generated by activesection 105A (e.g., AC power signals 108A and 108B) into DC electricalenergy (e.g., DC power signals 107A and 107B), which may be output ontoHVDC bus 114A. In some examples, DC power signals 107A and 107B may bereferred to as a first plurality of DC power signals. A total currentlevel of the first plurality of DC power signals (e.g., a combinedcurrent of DC power signals 107A and 107B) may be greater than 20 amps,100 amps, 200 amps, or more). As such, rectifiers 106A and 106B may forma first plurality of rectifiers configured to convert AC electricalenergy output by the first plurality of phase set windings (e.g., phaseset windings of active section 105A) into first DC electrical energy.Each of rectifiers 106A and 106B may covert power from separate phaseset windings of the first plurality of phase set windings. As such, eachphase set winding of the first plurality of phase set windings may bedriven by an independent rectifier unit. Similarly, rectifiers 106C and106D may convert AC electrical energy generated by active section 105B(e.g., AC power signals 108C and 108D) into DC electrical energy (e.g.,DC power signals 107C and 107D), which may be output onto HVDC bus 114B.As such, rectifiers 106C and 106D may form a second plurality ofrectifiers configured to convert AC electrical energy output by thesecond plurality of phase set windings (e.g., phase set windings ofactive section 105B) into second DC electrical energy. Each ofrectifiers 106C and 106D may covert power from separate phase setwindings of the second plurality of phase set windings. As such, eachphase set winding of the second plurality of phase set windings may bedriven by an independent rectifier unit. Further details of one exampleof a rectifier of rectifiers 106 are discussed below with reference toFIG. 4 .

Propulsion modules 118 may be configured to provide propulsive force(e.g., to propel a vehicle that includes system 100). Each of propulsionmodules 118 may include an electric motor of electric motors 120A and120B and a propulsor (e.g., fan, propeller, etc.) of propulsors 122A and122B. For instance, propulsion module 118A may include electric motor120A that rotates propulsor 122A, and propulsion module 118B may includeelectric motor 120B that rotates propulsor 122B. In some examples,electric motors 120 may include AC electric motors. In such examples,propulsion modules 118A may include inverters configured to convert DCelectrical energy (e.g., sourced from HVDC busses 114) into ACelectrical energy to drive the AC electric motors.

System 100 may include several electric busses, including control busses110, LVDC busses 112, and HVDC busses 114. Control busses 110 may beconfigured to transport data and/or control signals amongst componentsof system 100. For instance, control busses 110 may transport controlsignals amongst rectifiers 106. LVDC busses 112 may be configured toprovide low voltage DC electrical energy (e.g., 14 volts, 28 volts, 36volts, 48 volts, etc.) to various components of system 100. Forinstance, LVDC busses 112 may provide low voltage DC energy torectifiers 106 (e.g., to operate various components of rectifiers 106,such as controllers and active components). HVDC busses 114 may beconfigured to transport high voltage DC electrical energy (e.g., 270volts, 600 volts, 1080 volts, 2160 volts, etc.) to various components ofsystem 100. For instance, HVDC busses 114 may transport high voltage DCelectrical energy from rectifiers 106 to propulsion modules 118.

In some cases, such as the example of FIG. 1 , the electric busses maybe divided into multiple domains 109A and 109B (collectively, “domains109”), each of domains 109 may include a member of each electric bus.For instance, domain 109A may include control bus 110A, LVDC bus 112A,and HVDC bus 114A; and domain 109B may include control bus 110B, LVDCbus 112B, and HVDC bus 114B.

Components of system 100 may be assigned, and electrically connected to,at least one of the domains. Critical components, such as propulsionmodules 118, may be distributed across the domains. For instance,propulsion module 118A may be attached to domain 109A and receive powerfrom HVDC bus 114A (e.g., electric motor 120A may operate usingelectrical energy sourced from HVDC bus 114A), and propulsion module118B may be attached to domain 109B and receive power from HVDC bus 114B(e.g., electric motor 120B may operate using electrical energy sourcedfrom HVDC bus 114B). In this way, system 100 may include a plurality ofelectrical motors 120, a first sub-set of electrical motors 120 (e.g.,electrical motor 120A) may provide propulsion (e.g., propel an aircraftthat includes system 100) using electrical energy sourced via a first DCelectrical bus (e.g., HVDC bus 114A) and a second sub-set of electricalmotors 120 (e.g., electrical motor 120B) may provide propulsion (e.g.,propel the aircraft that includes system 100) using electrical energysourced via a second DC electrical bus (e.g., HVDC bus 114B). In thisway, critical components attached to a first domain can continueoperation even in the event of a complete failure of a second domain.For instance, propulsion module 118B may continue operation (e.g.,continue to provide propulsive force for a vehicle that includes system100) even if a failure occurs in domain 109A that results in no powerbeing output to HVDC bus 114A.

As generator 104 is driven by a prime mover (e.g., combustion motor102), output power of generator 104 may not be removable by simplyhalting action of rectifiers 106. It may be desirable for faultsinternal to machine generator 104 or in connecting AC cables (e.g.,cables that transport AC power signals 108) to not pose a safety risk(e.g., by overheating and compromising the insulation or structuralintegrity of the other segments). For this reason, many auxiliary powerunits (APU) installed on aircraft use field-wound rotor technology, orin the case of permanent magnet (PM) generators, may include a clutch todisengage driveshaft 103 upon detection of a fault. As PM generatorsprovide weight and efficiency benefits, it may be desirable forgenerator 104 to be a PM generator. Furthermore, a clutch may not bepractical as a single fault in one of active sections 105 wouldnecessitate a total loss of power, which would eliminate some of theadvantages of system 100 (e.g., the advantages of including multipleactive sections, independent rectifiers, and split HVDC busses).Therefore, parameters of generator 104 may be targeted to produce ashort circuit current of a similar magnitude to a nominal current. Inthis way, a fault in an AC segment (generator winding set, connectingcable set, or rectifier AC input) may persist indefinitely withoutposing a safety hazard, while the remaining phase sets can continue toproduce full power. The windings may be designed such that the windingsof one of active section 105 are physically separated from the other(see FIG. 2 ). Additionally, in some examples, each slot may be filledby a winding of only one phase (see FIG. 2 ), which may minimize risk offault occurring between two overlapping winding sets.

As discussed in further detail below, system 100 may react to certainfaults by decoupling and/or shutting down one or more of rectifiers 106.A fault in a particular rectifier of rectifiers 106 may only result in apower reduction of 25% (e.g., where rectifiers 106 includes fourrectifiers), leaving 75% of power generation capacity remaining. Assuch, system 100 may be considered to be fault tolerant without havingto fully duplicate a generation system.

FIG. 2 is a schematic diagram illustrating a cross-section of agenerator, in accordance with one or more aspects of this disclosure.Generator 204 of FIG. 2 may be an example of generator 104 of FIG. 1 .As shown in FIG. 2 , generator 204 may include stator 201 that includes205 active sections 205A and 205B (collectively, “active sections 205”),rotor 230, and position sensors 236A and 236B (collectively, “positionsensors 236”). Active sections 205 of FIG. 2 may be examples of activesections 105 of FIG. 1 .

Rotor 230 may be coupled to a combustion motor and may rotate usingrotational mechanical energy provided by the combustion motor. Forinstance, rotor 230 may include attachment portion 238 (illustrated asbeing splined) that is configured to receive rotational mechanicalenergy, such as from drive shaft 103 of combustion motor 102 of FIG. 1 .Rotor 230 may carry components that, when rotated, result in thegeneration of electrical power. For instance, rotor 230 may carrymagnetic components 232A and 232B (e.g., at or near an outer surface ofrotor 230). In some examples, rotor 230 may include a retaining bandconfigured to retain magnetic components 232.

As discussed above, generator 204 may be divided into multiple activesections 205. Each of active sections 205 may be electricallyindependent, but may utilize common rotor 230. For instance, rotation ofmagnetic components 232A may generate power in active section 205A androtation of magnetic components 232B may generate power in activesection 205B, but the power generated in active section 205A may beelectrically independent of the power generated in active section 205B.In this way, electrical power may be independently generated in multipleactive sections without requiring multiple heavy and/or expensivecombustion motors.

Each of active sections 205 may include a plurality of phase setwindings. For instance, as shown in FIG. 2 , active section 205A mayinclude first plurality of phase set windings 234A and active section205B may include second plurality of phase set windings 234B. Each ofactive sections 205 may include a respective plurality of slots, whichmay be occupied by a single-phase set winding. For instance, activesection 205A may include a first plurality of slots, and each slot ofthe first plurality of slots may be occupied by a single-phase setwinding of the first plurality of phase set windings. Similarly, activesection 205B may include a second plurality of slots, and each slot ofthe second plurality of slots may be occupied by a single-phase setwinding of the second plurality of phase set windings. One exampleallocation of phase set windings 234A/234B to slots of generator 204discussed below with reference to FIG. 3 .

Position sensors 236 may be configured to output signals that representa rotational position of rotor 230. In the example of FIG. 2 , positionsensors 236 may include a separate position sensor for each of activesections 205, each respective position sensor of position sensors 236providing an indication of the rotational position of rotor 230 torectifiers handling power output of the respective active section. Forinstance, position sensor 236A may provide an indication of therotational position of rotor 230 to rectifiers 106A and 106B of FIG. 1 ,and position sensor 236B may provide an indication of the rotationalposition of rotor 230 to rectifiers 106C and 106D of FIG. 1 . Byutilizing separate position sensors for each active section, faulttolerance may be further improved (e.g., as failure of a position sensorin an active section may not impact operation of other active sections).

In some examples, generator 204 may operate with a position sensorlesscontrol method (e.g., rectifiers may be controlled without knowledge ofa position of rotor 230). As such, in some examples, generator 204 mayomit position sensors 236.

FIG. 3 is a chart illustrating an example arrangement of windings inslots of an active section of a generator, in accordance with one ormore aspects of this disclosure. As discussed above, an active sectionof a generator, such as active section 105A of generator 104 of FIG. 1 ,may include a plurality of phase set windings (e.g., set A and set B).The phase set windings may be overlapping. For instance, windings of setA may be overlapping with windings of set B. AC electrical energygenerated by each of the plurality of phase set windings may be handledby a separate rectifier. For instance, AC electrical energy generated byset A (e.g., End winding ph1, End winding ph2, End winding ph3) may beconverted to DC by a first rectifier, and AC electrical energy generatedby set B (e.g., End winding ph4, End winding ph5, End winding ph6) maybe converted to DC by a second rectifier. In some examples, each slot ofan active section may be occupied (e.g., filled) by a winding of onlyone phase. Chart 300 of FIG. 3 illustrates one such allocation ofwindings to slots. By filling slots with windings of only one phase, therisk of fault occurring between two overlapping winding sets may beminimized.

FIG. 4 is a block diagram illustrating a rectifier of a fault tolerantgeneration system, in accordance with one or more aspects of thisdisclosure. Rectifier 406 of FIG. 4 may be an example of a rectifier ofrectifiers 106 of FIG. 1 . As shown in FIG. 4 , rectifier 406 mayinclude power stage 440, contactor 444, controller 446, and sensors 448.

Power stage 440 may be configured to covert alternating current (AC)electrical energy into direct current (DC) electrical energy. Forinstance, power stage 440 may convert input AC power signal 408 (e.g., athree-phase AC power signal including phases V₁, V₂, and V₃) into DCpower signal 407 (V_(DC)). In some examples, power stage 440 may be anactive rectifier that includes switches 442, the controlled switching ofwhich may perform the AC/DC conversion. For instance, power stage 440may be a three-phase active rectifier and switches 442 may be powerelectronic switches (e.g., either IGBTs with accompanying reverse diode,or MOSFETs) in a “6-pack” configuration.

Controller 446 may perform one or more operations to controlfunctionality of components of rectifier 406. For instance, where powerstage 440 is an active rectifier, controller 446 may output signals thatcontrol operation of switches 442. Controller 446 may generate thesignals that control operation of switches 442 based on various inputdata. Examples of input data include, but are not necessarily limitedto, rotation position data received from a position sensor (e.g., aposition sensor of position sensors 236 of FIG. 2 ), and data receivedfrom sensors 448. Controller 446 may be coupled to a control bus, suchas a control bus of control busses 110 of FIG. 1 . As discussed herein,controller 446 may apply a crowbar using switches 442. For instance,controller 446 may output signals to switches 442 that cause all ofswitches 442 to close at a particular time, thereby applying a crowbar.

Controller 446 may comprise any suitable arrangement of hardware,software, firmware, or any combination thereof, to perform thetechniques attributed to controller 446 herein. Examples of controller446 include any one or more microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), or any other equivalent integrated ordiscrete logic circuitry, as well as any combinations of suchcomponents. When controller 446 includes software or firmware,controller 446 further includes any necessary hardware for storing andexecuting the software or firmware, such as one or more processors orprocessing units.

In general, a processing unit may include one or more microprocessors,DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Although notshown in FIG. 4 , controller 446 may include a memory configured tostore data. The memory may include any volatile or nonvolatile media,such as a random access memory (RAM), read only memory (ROM),nonvolatile RAM (NVRAM), electrically erasable programmable ROM(EEPROM), flash memory, and the like. In some examples, the memory maybe external to controller 446 (e.g., may be external to a package inwhich controller 446 is housed).

Sensors 448 may be configured to sense various parameters of rectifier448. Example parameters that may be sensed by sensors 448 include, butare not limited to, input current (e.g., a current of one or more of Vi,V₂, and V₃), input voltage (e.g., a voltage of one or more of Vi, V₂,and V₃), output current (e.g., a current of V_(DC)), output voltage(e.g., a voltage of V_(DC)), and a temperature of rectifier 406.

As discussed above, switches 442 may be IGBT or MOSFET switches. Bothswitch types (IGBT and MOSFET) may be considered to be “uni-directionalblocking”, which means that switches 442 may not be able to be used toblock current from flowing into a fault on the HVDC bus. While a faultwithin one of HVDC busses 114 may lead to 50% power loss, it isdesirable for such a fault to not pose a safety hazard (e.g., to anaircraft propelled by system 100). As discussed above, it may not bepossible to remove the energy source mechanically orelectromagnetically. As such, it may be desirable to include some meansto electrically isolate outputs of rectifier 406 from HVDC busses 114.However, breaking a DC fault may be more difficult than breaking an ACfault (e.g., due to the lack of a zero-crossing in the current waveform(upon a zero-crossing in an AC fault, the arc will naturallyextinguish)). DC circuit breakers suitable for aerospace applicationsmay not be available above 28V and circuit breakers compatible with thevoltage (270 volts, 1 kV or greater) and fault current (e.g., 20 amps,100 amps, or greater) may not meet weight and environmental tolerancerequirements desirable for airborne applications.

In accordance with one or more aspects of this disclosure, rectifier 406may include contactor 444 that may be configured to electricallyde-couple DC output of rectifier 406 from HVDC electrical busses. Forinstance, when contactor 444 is closed, output of power stage 444 may beelectrically coupled to HVDC bus 114 (e.g., such that DC power signal407′ flows through contactor 444 and to HVDC bus 114 as DC power signal407). However, when contactor 444 is open, output of power stage 444 maybe electrically de-coupled from HVDC bus 114 (e.g., such that DC powersignal 407′ is prevented from flowing through contactor 444 and to HVDCbus 114).

Contactor 444 may be rated to handle a certain current level. Increasinga current level rating of a contactor, such as contactor 444, may resultin an increase in size and/or weight of the contactor. As discussedabove, electrical current of an active section of a generator may bedivided amongst multiple rectifiers. Such an arrangement may reduce anamount of current that flows through each rectifier. For instance, inthe example of FIG. 1 , 50% of the current generated by active section105A may flow through each of rectifiers 106A and 106B (e.g., electricalcurrent of a plurality of DC electrical signals generated from a singleactive section may be divided amongst a set of rectifiers). As such, thefault tolerant generation system of this disclosure may enable use ofsmaller and/or lighter contactors.

In some examples, operation of contactor 444 may be controlled bycontroller 446. For instance, controller 446 may selectively outputsignals that cause contactor 444 to open and close. During normaloperation, controller 446 may cause contactor 444 to remain closed(e.g., such that output of power stage 440 is electrically coupled toHVDC bus 114). However, responsive to detection of certain faults,controller 446 may cause contactor 444 to open (e.g., such that outputof power stage 440 is electrically de-coupled from HVDC bus 114). Byutilizing controller 446 (i.e., a controller already included inrectifier 406) to control operation of contactor 444, inclusion of anadditional contactor controller may be avoided. In this way, thisdisclosure may reduce cost and complexity of a fault tolerant generationsystem.

In some examples, controller 446 may perform one or more operations toreduce a stress on contactor 444. As one example, controller 446 maytime an opening of contactor 444 to coincide with a minimum in thecurrent through contactor 444. As another example, controller 446 mayperform a 3 phase short or other action (e.g., via switches 442) toreduce a current through contactor 444 momentarily. As such, controller446 may provide for a reduction of stress on contactor 444 whencontactor 444 opens, thereby increasing a life of contactor 444 and/orenabling use of smaller/lighter/cheaper contactors as contactor 444.

Controller 446 may detect faults based at least in part on datagenerated by sensors 448. For instance, controller 446 may detectoccurrence of a three-phase short fault based at least in part on avoltage or a current measurement sensed by sensors 448. By utilizingsensors 448 (i.e., sensors already included in rectifier 406) to detectfault occurrence, inclusion of redundant sensors may be avoided. In thisway, this disclosure may reduce cost and complexity of a fault tolerantgeneration system.

As discussed above, rectifier 406 may be an example of a rectifier ofrectifiers 106 of FIG. 1 . It should be understood that each ofrectifiers 106 may include components similar to rectifier 406 of FIG. 4. For instance, each respective rectifier of rectifiers 106 may includea respective power stage (including respective switches), a respectivecontactor, a respective controller, and respective sensors. As such, afirst set of rectifiers may include a first set of active rectifiersthat convert a first plurality of AC electrical signals into a firstplurality of DC electrical signals for output onto a first DC electricalbus of the plurality of DC electrical busses; each of the first set ofactive rectifiers may include switches; a second set of rectifiers mayinclude a second set of active rectifiers that convert a secondplurality of AC electrical signals into a second plurality of DCelectrical signals for output onto a second DC electrical bus of theplurality of DC electrical busses; and each of the second set of activerectifiers comprises switches.

In accordance with one or more aspects of this disclosure, controllersof various rectifiers may be configured to perform a coordinatedresponse to certain faults. A metallic retaining band and permanentmagnets of a rotor (e.g., of rotor 230 of FIG. 2 ) may have inducedlosses when exposed to any non-synchronous magnetic field (i.e., anyfield seen from the rotor reference frame that is time-varying). Therotor losses may be small in healthy operation. For instance, in normal/ healthy operation, the only induced losses may be due to harmonicsself-induced by the generator electromagnetic construction, and theharmonics contained within the switching voltage waveform applied by therectifier. While the rotor losses are manageable in healthy operation,faults that create an unbalanced field may result in excessive heatgeneration in the rotor, potentially leading to mechanical failure thatcompromises the entire generator. A two-phase short (i.e., a shortbetween one phase and another winding the winding set, a turn-turnshort, and a star-star short (i.e., a short that occurs between twooverlapping winding sets), are included in such faults that may causeadditional rotor heating (e.g., faults that create an unbalanced field).

In these cases, rectifiers 106 associated with a particular activesection of active sections 105 may detect faults and, in a coordinatedmanner actively apply a three-phase short with rectifiers controllingthe affected active section (e.g., coordinate response to detectedfaults). For instance, rectifiers of rectifiers 106 attached to activesection 105A (e.g., rectifiers 106A and 106B) may coordinate response tofaults within the rectifiers attached to active section 105A. Similarly,rectifiers of rectifiers 106 attached to active section 105B (e.g.,rectifiers 106C and 106D) may coordinate response to faults within therectifiers attached to active section 105B. In this way, the magneticfield seen by the rotor can be re-balanced to avoid rotor failure.

All rectifiers corresponding to the faulted active section may performthe action in order to minimize the rotor heating by eliminating inaddition the normally existing harmonic rotor losses induced by therectifier. In some examples, the performance of coordinated faultresponse may be improved by selecting generator parameters to achieveshort circuit current achieved by the generator parameters (e.g., whichmay allow the power electronic switches in the rectifier (e.g., switches442) to endure an applied three-phase short (the fault current will flowthrough the rectifier switches) indefinitely without overheating).

FIG. 5 is a chart illustrating example responses to rectifier faults, inaccordance with one or more aspects of this disclosure. The faultresponses of table 500 of FIG. 5 may be performed by a controller of arectifier, such as controller 446 of rectifier 406.

In fault cases where a coordinated response is performed (e.g., faultsthat create an unbalanced field), the power loss may be 50% (where thegenerator includes two active sections). In fault cases where acoordinated response is not performed, the power loss may only be 25%.Table 500 illustrates examples of faults for which controllers ofrectifiers may perform a coordinated response vs faults for which thecontrollers may not perform such a coordinated response. As shown intable 500, a controller of a rectifier (e.g., controller 446 ofrectifier 406) may perform a coordinated response (e.g., applythree-phase short and cause controllers of other rectifiers attached tothe same active section to apply three-phase short) include three-phaseshort to ground, three-phase short, two-phase short to ground, two-phaseshort, one-phase short, and star to star fault.

As also shown in table 500, a controller of a rectifier (e.g.,controller 446 of rectifier 406) may isolate HVDC terminals for a widerange of faults (e.g., a super set of those faults for which thecontroller may perform a coordinated response). The controller mayisolate the HVDC terminals by causing a contactor within the rectifierto open. For instance, controller 446 may isolate HVDC terminals ofrectifier 406 by causing contactor 444 to open.

FIG. 6 is a flowchart illustrating an example technique for faulthandling in a fault tolerant generation system, in accordance with oneor more aspects of this disclosure. The technique of FIG. 6 may beperformed by a controller of a rectifier, such as controller 446 ofrectifier 406 of FIG. 4 .

Controller 446 may monitor one or more parameters of rectifier 406(602). For instance, controller 446 may receive data from sensors 448that represents one or more operating parameters of rectifier 406.

Controller 446 may determine whether a fault has occurred (604). Forinstance, controller 446 may determine, based on the data received fromsensors 448, whether a fault has occurred.

Responsive to determining that a fault has occurred (“Yes” branch of604) controller 446 may determine a response to the fault. For instance,controller 446 may determine a response to the fault based on a type ofthe determined fault in accordance with table 500 of FIG. 5 . As oneexample, controller 446 may cause a contactor (e.g., contactor 444) ofrectifier 406 to open, thereby electrically de-coupling rectifier from aHVDC bus.

In some examples, as discussed above, controller 446 may determinewhether to perform a coordinated response to the fault with one or moreother rectifiers (608). For instance, where the fault is of a type thatwill create an unbalanced field in a generator, controller 446 maydetermine to perform the coordinated response.

Responsive to determining to perform the coordinated response (“Yes”branch of 608), controller 446 may perform the coordinated response. Forinstance, controller 446 may output a signal to one or more otherrectifiers attached to a same active section as rectifier 406 requestingthat the one or more other rectifiers apply a three-phase short (e.g.,apply crowbar).

The following examples may illustrate one or more aspects of thedisclosure:

Example 1A. A turbo-generator system for generating propulsiveelectrical power for an aircraft, the turbo-generator system comprising:an electric machine comprising: a rotor configured to be rotated by agas-turbine of the turbo-generator system; a stator comprising: a firstactive section comprising first windings surrounding a first portion ofthe rotor; and a second active section comprising second windingssurrounding a second portion of the rotor.

Example 2A. The turbo-generator system of example 1A, wherein: the firstwindings comprise a first plurality of phase set windings; and thesecond windings comprise a second plurality of phase set windings.

Example 3A. The turbo-generator system of example 2A, furthercomprising: a first plurality of rectifiers configured to convertalternating current (AC) electrical energy output by the first pluralityof phase set windings into first direct current (DC) electrical energy;and a second plurality of rectifiers configured to convert AC electricalenergy output by the second plurality of phase set windings into secondDC electrical energy.

Example 4A. The turbo-generator system of example 3A, wherein: the firstplurality of rectifiers is configured to output the first DC electricalenergy onto a first DC electrical bus; and the second plurality ofrectifiers is configured to output the second DC electrical energy ontoa second DC electrical bus.

Example 5A. The turbo-generator system of example 4A, wherein theaircraft includes a plurality of electrical motors configured to propelthe aircraft, wherein a first sub-set of the plurality of electricalmotors are configured to propel the aircraft using electrical energysourced via the first DC electrical bus, and wherein a second sub-set ofthe plurality of electrical motors are configured to propel the aircraftusing electrical energy sourced via the second DC electrical bus.

Example 6A. The turbo-generator system of any of examples 3A-5A, furthercomprising: a first position sensor configured to output a firstindication of a rotational position of the rotor to the first pluralityof rectifiers; and a second position sensor configured to output asecond indication of the rotational position of the rotor to the secondplurality of rectifiers.

Example 7A. The turbo-generator system of any of examples 2A-6A,wherein: the first active section comprises a first plurality of slots,each slot of the first plurality of slots is occupied by a single phaseset winding of the first plurality of phase set windings, the secondactive section comprises a second plurality of slots, and each slot ofthe second plurality of slots is occupied by a single phase set windingof the second plurality of phase set windings.

Example 8A. The turbo-generator system of any of examples 1A-7A, whereinthe first active section operates as a first permanent magnet (PM)generator, and wherein the second active section operates as a second PMgenerator.

Example 9A. The turbo-generator system of any of examples 1A-8A, whereinthe turbo-generator system does not include a clutch configured torotationally de-couple the rotor from the gas-turbine.

Example 10A. An airframe comprising the turbo-generator system of any ofexamples 1A-9A.

Example 1B. A system for providing propulsive electrical power for anaircraft, the system comprising: a first generator configured to outputa first plurality of alternating current (AC) electrical signals; asecond generator configured to output a second plurality of ACelectrical signals; a first set of rectifiers of a plurality ofrectifiers, wherein the first set of rectifiers are configured toconvert the first plurality of AC electrical signals into a firstplurality of direct current (DC) electrical signals for output onto afirst DC electrical bus of a plurality of DC electrical busses, whereinelectrical current of the first plurality of DC electrical signals isdivided amongst the first set of rectifiers, and wherein each respectiverectifier of the first set of rectifiers includes a respective contactorconfigured to de-couple a DC output of the respective rectifier from thefirst DC electrical bus; and a second set of rectifiers of the pluralityof rectifiers, wherein the second set of rectifiers are configured toconvert the second plurality of AC electrical signals into a secondplurality of DC electrical signals for output onto a second DCelectrical bus of the plurality of DC electrical busses, whereinelectrical current of the second plurality of DC electrical signals isdivided amongst the second set of rectifiers, and wherein eachrespective rectifier of the second set of rectifiers includes arespective contactor configured to de-couple a DC output of therespective rectifier from the second DC electrical bus.

Example 2B. The system of example 1B, wherein each rectifier of theplurality of rectifiers includes: a power stage configured to convertinput AC electrical signals to an output DC electrical signal; and acontroller configured to control operation of the power stage therectifier and the contactor of the rectifier.

Example 3B. The system of example 2B, wherein the power stages of theplurality of rectifiers comprise switches, wherein, to control operationof a power stage of a particular rectifier, a controller of theparticular rectifier is configured to control operation of switches ofthe power stage of the particular rectifier.

Example 4B. The system of example 2B or 3B, wherein each rectifier ofthe plurality of rectifiers further includes: one or more sensors,wherein, to control operation of a power stage of a particular rectifierand a contactor of the particular rectifier, the controller of theparticular rectifier is configured to control, based on output generatedby one or more sensors of the particular rectifier, operation of thepower stage of the particular rectifier and the contactor of theparticular rectifier.

Example 5B. The system of any of examples 2B-4B, wherein, to controloperation of a contactor of a particular rectifier, the controller ofthe particular rectifier is configured to cause the contactor of theparticular rectifier to open responsive to detecting a fault in theparticular rectifier.

Example 6B. The system of any of examples 1B-5B, wherein a voltage levelof the plurality of DC electrical busses is greater than 270 volts.

Example 7B. The system of any of examples 1B-5B, wherein total a currentlevel of the first plurality of DC electrical signals is greater than 20amps.

Example 8B. The system of any of examples 1B-7B, wherein the first andsecond generator are integrated into a single stator surrounding asingle rotor.

Example 9B. The system of any of examples 1B-8B, wherein the aircraftincludes a plurality of electrical motors configured to propel theaircraft, wherein a first sub-set of the plurality of electrical motorsare configured to propel the aircraft using electrical energy sourcedvia the first DC electrical bus, and wherein a second sub-set of theplurality of electrical motors are configured to propel the aircraftusing electrical energy sourced via the second DC electrical bus.

Example 10B. An airframe comprising the turbo-generator system of any ofexamples 1B-9B.

Example 11B. A method comprising: monitoring, by a controller of arectifier of first set of rectifiers attached to an active section of agenerator of a system that provides propulsive electrical power for anaircraft, one or more parameters of the rectifier; determining, by thecontroller and based on the one or more parameters, whether a fault hasoccurred in the rectifier; and responsive to determining that the faulthas occurred in the rectifier, causing a contactor included in therectifier to de-couple a DC output of the rectifier from a first DCelectrical bus.

Example 12B. The method of example 11B, wherein the rectifier is anactive rectifier that includes a power stage comprising switches, themethod further comprising: controlling, by the controller, the switches.

Example 13B. The method of example 12B, wherein monitoring the one ormore parameters of the rectifier comprises: receiving, by thecontroller, data from one or more sensors of the rectifier, whereincontrolling the switches comprises controlling the switches based on thereceived data, and wherein determining whether the fault has occurredcomprises determining whether the fault has occurred based on thereceived data.

Example 1C. A system for providing propulsive electrical power for anaircraft, the system comprising: a first generator configured to outputa first plurality of alternating current (AC) electrical signals; asecond generator configured to output a second plurality of ACelectrical signals; a first set of rectifiers of a plurality ofrectifiers, wherein the first set of rectifiers are configured toconvert the first plurality of AC electrical signals into a firstplurality of direct current (DC) electrical signals for output onto afirst DC electrical bus of a plurality of DC electrical busses; and asecond set of rectifiers of the plurality of rectifiers, wherein thesecond set of rectifiers are configured to convert the second pluralityof AC electrical signals into a second plurality of DC electricalsignals for output onto a second DC electrical bus of the plurality ofDC electrical busses, wherein each rectifier of the plurality ofrectifiers includes a respective controller of a plurality ofcontrollers, and wherein the plurality of controllers are configured tocoordinate response to detected faults.

Example 2C. The system of example 1C, wherein, to coordinate response todetected faults, the plurality of controllers are configured toseparately coordinate response to faults that create an unbalancedfield.

Example 3C. The system of example 1C or example 2C, wherein, tocoordinate response to detected faults, the plurality of controllers areconfigured to separately coordinate response to faults detected withinthe first set of rectifiers and faults detected within the second set ofrectifiers.

Example 4C. The system of example 3C, wherein the first set ofrectifiers comprise a first set of active rectifiers that convert thefirst plurality of AC electrical signals into the first plurality of DCelectrical signals for output onto the first DC electrical bus of theplurality of DC electrical busses; each of the first set of activerectifiers comprises switches; the second set of rectifiers comprise asecond set of active rectifiers that convert the second plurality of ACelectrical signals into the second plurality of DC electrical signalsfor output onto the second DC electrical bus of the plurality of DCelectrical busses; and each of the second set of active rectifierscomprises switches.

Example 5C. The system of example 4C, wherein, to separately coordinateresponse to faults detected within the first set of rectifiers, acontroller of a first rectifier of the first set of rectifiers isconfigured to apply a crowbar using switches of the first rectifier andcause a controller of a second rectifier of the first set of rectifiersto apply a crowbar using switches of the second rectifier.

Example 6C. The system of example 5C, wherein, to separately coordinateresponse to faults detected within the second set of rectifiers, acontroller of a second rectifier of the second set of rectifiers isconfigured to apply a crowbar using switches of the first rectifier ofthe second set of rectifiers and cause a controller of a secondrectifier of the second set of rectifiers to apply a crowbar usingswitches of the second rectifier of the second set of rectifiers.

Example 7C. The system of any of examples 2C-6C, wherein faults thatcreate an unbalanced field include one or more of: a three-phase short;a two-phase short; a one-phase short; and a star to star fault.

Example 8C. The system of any of examples 1C-7C, wherein the first andsecond generator comprise permanent magnet generators.

Example 9C. The system of any of examples 1C-8C, wherein the first andsecond generator are integrated into a single stator surrounding asingle rotor.

Example 10C. The system of any of examples 1C-9C, wherein the aircraftincludes a plurality of electrical motors configured to propel theaircraft, wherein a first sub-set of the plurality of electrical motorsare configured to propel the aircraft using electrical energy sourcedvia the first DC electrical bus, and wherein a second sub-set of theplurality of electrical motors are configured to propel the aircraftusing electrical energy sourced via the second DC electrical bus.

Example 11C. An airframe comprising the turbo-generator system of any ofexamples 1C-10C.

Example 12C. A method comprising: monitoring, by a controller of arectifier of first set of rectifiers attached to an active section of agenerator of a system that provides propulsive electrical power for anaircraft, one or more parameters of the rectifier; determining, by thecontroller and based on the one or more parameters, whether a fault hasoccurred in the rectifier; responsive to determining that the fault hasoccurred in the rectifier, determining, by the controller, a response tothe fault, wherein determining the response to the fault comprisesdetermining whether to perform a coordinated response to the fault withanother rectifier of the first set of rectifiers; and responsive todetermining to perform the coordinated response to the fault,performing, by the controller, the coordinated response.

Example 13C. The method of example 12C, wherein determining whether toperform the coordinated response to the fault with the other rectifierof the first set of rectifiers comprises determining to perform thecoordinate response responsive to determining that the fault will createan unbalanced field in the generator.

Example 14C. The method of example 12C or example 13C, whereinperforming the coordinated response comprises applying a crowbar usingswitches of the rectifier and causing a crowbar to be applied usingswitches of the other rectifier.

Example 15C. The method of any of examples 12C-14C, wherein performingthe coordinated response comprises performing the coordinated responseindependently of rectifiers of a second set of rectifiers attached toanother active section of the generator.

Various examples have been described. These and other examples arewithin the scope of the following claims.

1. A turbo-generator system for generating propulsive electrical powerfor an aircraft, the turbo-generator system comprising: an electricmachine comprising: a rotor configured to be rotated by a gas-turbine ofthe turbo-generator system; a stator comprising: a first active sectioncomprising first windings surrounding a first portion of the rotor; anda second active section comprising second windings surrounding a secondportion of the rotor; one or more rectifiers configured to convertalternating current (AC) electrical energy output by the first windingsinto first direct current (DC) electrical energy and output the first DCelectrical energy onto a first DC electrical bus; and one or more ofrectifiers configured to convert AC electrical energy output by thesecond windings into second DC electrical energy and output the secondDC electrical energy onto a second DC electrical bus, wherein theaircraft includes a plurality of electrical motors configured to propelthe aircraft, wherein a first sub-set of the plurality of electricalmotors are configured to propel the aircraft using electrical energysourced via the first DC electrical bus, and wherein a second sub-set ofthe plurality of electrical motors are configured to propel the aircraftusing electrical energy sourced via the second DC electrical bus.
 2. Theturbo-generator system of claim 1, wherein: the first windings comprisea first plurality of phase set windings; and the second windingscomprise a second plurality of phase set windings. 3-6. (canceled) 7.The turbo-generator system of claim 2, wherein: the first active sectioncomprises a first plurality of slots, each slot of the first pluralityof slots is occupied by a single phase set winding of the firstplurality of phase set windings, the second active section comprises asecond plurality of slots, and each slot of the second plurality ofslots is occupied by a single phase set winding of the second pluralityof phase set windings.
 8. The turbo-generator system of claim 1, whereinthe first active section operates as a first permanent magnet (PM)generator, and wherein the second active section operates as a second PMgenerator.
 9. The turbo-generator system of claim 1, wherein theturbo-generator system does not include a clutch configured torotationally de-couple the rotor from the gas-turbine.
 10. An airframecomprising: a turbo-generator system comprising: an electric machinecomprising: a rotor configured to be rotated by a gas-turbine of theturbo-generator system; a stator comprising: a first active sectioncomprising first windings surrounding a first portion of the rotor; anda second active section comprising second windings surrounding a secondportion of the rotor; a first plurality of rectifiers configured toconvert alternating current (AC) electrical energy output by the firstactive section into first direct current (DC) electrical energy; and asecond plurality of rectifiers configured to convert AC electricalenergy output by the second active section into second DC electricalenergy, wherein the first plurality of rectifiers output the first DCelectrical energy onto a first DC bus, wherein the second plurality ofrectifiers output the second DC electrical energy onto a second DC bus,and wherein the airframe further comprises: a first propulsion moduleconfigured to propel the airframe using electrical energy sourced viathe first DC bus; and a second propulsion module configured to propelthe airframe using electrical energy sourced via the second DC bus. 11.(canceled)
 12. A turbo-generator system for generating propulsiveelectrical power for an aircraft, the turbo-generator system comprising:an electric machine comprising: a rotor configured to be rotated by agas-turbine of the turbo-generator system, the rotor comprisingpermanent magnets; a stator comprising: a first active sectioncomprising first windings surrounding a first portion of the rotor; anda second active section comprising second windings surrounding a secondportion of the rotor; and a controller configured to selectively applycrowbar to one of the first or second active sections.
 13. Theturbo-generator system of claim 12, further comprising: one or morerectifiers configured to convert alternating current (AC) electricalenergy output by the first windings into first direct current (DC)electrical energy and output the first DC electrical energy onto a firstDC electrical bus; and one or more rectifiers configured to convert ACelectrical energy output by the second windings into second DCelectrical energy and output the second DC electrical energy onto asecond DC electrical bus, wherein the aircraft includes a plurality ofelectrical motors configured to propel the aircraft, wherein a firstsub-set of the plurality of electrical motors are configured to propelthe aircraft using electrical energy sourced via the first DC electricalbus, and wherein a second sub-set of the plurality of electrical motorsare configured to propel the aircraft using electrical energy sourcedvia the second DC electrical bus.
 14. The turbo-generator system ofclaim 12, wherein the turbo-generator system does not include a clutchconfigured to rotationally de-couple the rotor from the gas-turbine. 15.The turbo-generator system of claim 1, further comprising a controllerconfigured to selectively mitigate a fault in one of the first or secondactive sections.
 16. The airframe of claim 10, further comprising: afirst position sensor configured to output a first indication of arotational position of the rotor to the first plurality of rectifiers;and a second position sensor configured to output a second indication ofthe rotational position of the rotor to the second plurality ofrectifiers.